using System;
public class Program
{
public static void Main()
int k = 10;
int count = 0;
int[] arr = new int[]{3,5,2,1,-3,7,8,15,6,13};
for(int i = 0;i<arr.Length;i++)
for(int j = i+1;j<arr.Length;j++)
if(arr[i]+arr[j] == k)
count++;
}
Console.WriteLine("Count of pairs whose sum is k :"+count);